Conventionally, a phase-control switching apparatus has been known that can suppress the generation of a transient voltage or current to the minimum by predicting a residual magnetic flux for each phase of a three-phase transformer based on the cutoff sequence of the three-phase transformer that is connected to an electric power system via a breaker and by closing the breaker at an optimum timing according to the predicted residual magnetic flux (for example, Patent Document 1).
Moreover, a phase-control switching apparatus has been known that can suppress the generation of a transient voltage or current to the minimum by calculating a residual magnetic flux for each phase of a transformer when a breaker receives an open instruction that acts as a trigger and by closing the breaker at an optimum timing according to the calculated residual magnetic flux (for example, Patent Document 2). In this case, the residual magnetic flux is calculated based on a voltage value for each phase of the transformer around the reception of the open instruction that is measured by a voltage measuring unit located on the transformer side of the breaker for each phase.
Patent Document 1: Japanese Patent Application Laid-open No. 2001-218354 (FIG. 1, FIG. 4, etc.)
Patent Document 2: Japanese Patent Application Laid-open No. 2005-204368 (FIG. 1, FIG. 2, etc.)